A railroad locomotive may be coupled to a railcar by motoring the locomotive into the railcar at a relative speed of about two miles per hour to engage the respective couplers on the locomotive and the railcar. Once coupling has been achieved, the throttle setting of the locomotive must be reduced to avoid spinning of the locomotive drive wheels, since the speed of the locomotive will be suddenly reduced as a result of the contact with the railcar. The reduction in speed of the locomotive will be a function of the relative mass of the locomotive plus any railcars already moving with the locomotive to the mass of the railcar being coupled and any other railcars already coupled to that railcar. For example, a locomotive being coupled to a single empty railcar will experience a relatively small speed decrease due to the contact with the railcar, whereas a locomotive being coupled to a long string of heavily loaded railcars will experience a more dramatic decrease in speed upon being coupled.
A locomotive engineer must pay attention to the distance between the locomotive and the railcar to be coupled in order to be prepared to reduce the throttle upon making contact. This activity can distract the engineer from other activities that can affect the safe and/or efficient operation of the locomotive. The task of coupling is made even more difficult if the engineer is operating the locomotive by remote control, as is often done in rail switching yards using a locomotive remote control system such as those sold by Canac, Inc. of Montreal, Canada, under the trademark Beltpack. Remote control systems generally utilize a transmitter unit remote from the locomotive that allows an operator to send commands or control signals to the receiver unit on the locomotive. The receiver unit then implements the commands for control systems of the locomotive, such as the braking system, throttle, and the like. While an engineer riding on a locomotive can actually feel the impact made with the coupled car, an operator of a remote control system has no such sense of feel and must rely on visual and audio observations only. This can be extremely difficult when the locomotive being controlled is operating at a substantial distance from the location of the operator.